1. Field of Invention
This invention relates to isometric strength testing apparatus and method, and more particularly relates to isometric strength testing for measuring disease progression in ALS patients.
2. Background
In the past decade, the number of candidate therapeutic agents for the treatment of ALS has greatly increased, and the ability of the clinical trial community to test these agents is limited due to cost, time, and especially resource constraints. Muscle strength is an important determinant of function in ALS and thus is a valuable outcome measure in clinical trials. Establishing a disease progression rate for each individual provides an extremely accurate method to determine even modest therapeutic effects. The equipment heretofore available to perform such tests is expensive and/or requires a highly trained evaluator.
Sample size determination is largely dependent on the variance of both the measurement system and the between-subject variation. Therefore, selection of the precise outcome measures is a critically important component of clinical trial design. Because strength loss within each subject is very linear, the variation of loss in a particular patient is very small. However, the differences in disease progression rates can be ten-fold or greater between subjects. By establishing each subject's rate of strength loss and comparing each subject to themselves, the sample size requirements are a fraction of the size needed to compare groups of subjects due to the variance of both the measurement system and the between subject variation employed in clinical trials today. Precise, accurate testing of muscle strength may allow much more efficient outcome measure and enable clinical trials to be significantly shorter, less expensive and require considerably less resources.
In accordance with one ALS testing protocol presently used, strength measurement of 18 muscle groups use maximal voluntary isometric contraction (MVIC). A measurement utilizes a strain gage attached to uprights and the subject pulls against a strap attached to the uprights to measure force output of several muscles in the arms and legs. However, this protocol is time intensive, requires the subject to be moved onto a treatment table and undergo multiple position changes during the testing procedure. The equipment used is large consuming substantial floor space, is very difficult to relocate and the cost of the equipment is substantial. Moreover, the testing protocol requires a highly trained evaluator. Furthermore, many subjects discontinue testing due to the difficulty with transfers and positioning as their disease worsens. As a result, many subjects are not tested in the later stages of the disease.
An alternative method to measure muscle strength uses hand-held dynamometry. This method uses a hand-held force gage to measure the force of the subject's muscular resistance. Holding the force gage in his hand, the evaluator attempts to break the subject's resistance. This method is relatively inexpensive, is portable and can be performed in the sitting position in a short time. However, because the force output is dependent on the evaluator overpowering the subject's strength and because many muscles are tested in an anti-gravity position, there are potentially extraneous factors reflected in the measurement. Moreover, testing positions and stabilization by the evaluator make standardization difficult to achieve.